Testing system



June 11, 1929., D, A NNETT 1.716.437

TESTING SYSTEM Filed Sept. 17, 192'? IN VEN TOR.

Z; K 60am ATTORNEY Patented June 11,1929.

UNITED STATES PATENT OFFICE.

IDANFORTE K. GANNETT, OF JACKSON HEIGHTS, NEW YORK, ASSIGNOR T AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TESTING SYSTEM.

This invention relates to electrical systems, and particularly to circuits for comparing the frequencies of currents of two or more electrical sources.

One .of the objects of this invention is to compare two inaudible frequencies to determine whether they are equal. This object may be accomplished by means of a detecting device, such as a telephone receiver, upon which is impressed an audible frequency modulated successivel by each inaudible fre quency, the audible requency being within the range of reception of the detecting device, such as the telephone receiver.

It is another object of this invention to permit two or more inaudible frequencies to modulate or otherwise modify the current of the audible frequency in accordance with the currents of two or more inaudible fre quencies which are to be compared to determine whether these frequencies are in synchronism, a detecting device which detects the presence or absence of current of -the audible frequency being employed to observe whether or not the frequencies to be' compared are in synchronism.

While this invention will be pointed out with particularity in the appended claims, the invention itself, both as to its further objects and features, will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawing in which Figure 1 represents one embodiment of the invention employing polar relays, and Fig.

2 represents another embodiment of the invention employing vacuum tubes.

Referring to Fig. 1 of the drawing, two sources of current designated by the referonce characters S and S are shown, the frequencies of these sources being below the range of audibility. Sources S and S may be vacuum tube oscillators, electrical vibrators, generators, or the like. Source S 1s connected to the winding of the polar relay P,, the armature of polar relay P vibrating between fixed contacts at the period of the current of the source S,. Source S is connected to the winding of a polar relay P 50. the armature of polar relay P vibrating between fixed contacts at the period of the current of source 8,. One of the fixed contacts of olar relay P is directly connected to one o the fixed, contacts of polar relay P Another source of current is designated I by reference character S This source of current may also be a vacuum tube oscillator, an electrical vibrator, a generator, or the like. One terminal of source S is connected to a detecting device designated by the reference character R, the detecting device B being a telephone receiver or headset or any other device capable of detecting current of an audible frequency. The wave emitted by source S is preferably a wave of an audible frequency which may easily be detected by the detecting device R. In other words, the frequency of a current of source S lies within the range of audibility of the telephone receiver representing the detecting device of this invention. The detecting device R is connected in series relationship with the source S between the armatures of polar relays P and P Thus, the armatures of polar relays P and P are connected in .a series circuit with the detecting device R and the source S when the armature of polar relay P closes its lower contact and the armature of the polar relay P closes its upper contact. When the lower and up er contacts of polar relays P and P are c osed by their respective armatures, current of the frequency of source S, is transmitted through the detecting device R, causing an audible sound. When either of the armatures of polar relays P and P opens the above mentioned series circuit, no current will flow through the detecting device R and, accordingly, there will be a period of silence.

If the currents emitted by sources S and S are of equal frequency, then the armatures of polar relays P and P will vibrate at the same frequency between their fixedcontacts. Then, if the armatures 'of polar relays P and P are 180 degrees out of phase while 05 vibrating at the same speed pulses of cur rent will pass through the detecting device R, the period of these pulses corresponding I to the period of either of the sources S or S Thus, if source S transmits current of a frequency, for example, of 20 cycles per second, current will pass through the detecting device R in pulses of equal duration twenty times per second, the current'of each pulse having a frequency corresponding to the frequency of source 8,. A degree phase difference between the armatures of polarrelays P and P, exists when the armature of polar relay P, closes its lower c011- tact while the armature of polar relay P closes its upper contact.

On the other hand, if the current of sources S and S are of equal frequency, causing the vibration of the armatures of polar relays P, and P in synchronism and not out of phase by 180 degrees, then the circuit interconnecting source S with the detecting device R will remain open so that no current passes through the detecting device R. Accordingly, there will be prolonged silence, no current, and particularly no current of an audible frequency, passing through the detecting device R. Thus, it will be apparent that the detecting device R may be employed to observe and compare the frequencies of the currents of sources S and S to determine whether these frequencies are substantially equal. If the frequencies of sources S and S are substantially equal, then there will be either a prolonged period of silence at the telephone receiver, acting as a detecting device, or there will be pulsations at regular intervals of equal duration at device R, the current of each pulsation being of an audible frequency within the range readilyreceivable by the detecting device R.

If, however, the frequencies of the currents transmitted by the sources S and S are not equal, pulsations of current will be transmitted through the detecting device R, these pulsations taking place at regular intervals, but having a duration which changes from instant to instant from zero to the entire length of the period of pulsation, the current passing through the detecting device R having a frequency within the audible range.

Thus, when sources S and S transmit currents which are not alike in frequency, the vibratory eriods of polar relays P and P will differ rom each other by an amount corresponding to the frequency difference between the currents of sources S and S producing audible sounds at the detecting device R of varying durations. The audible period at the detecting device R under these conditions varies from one of silence to one of a strong warble, and gives an effect on the listener somewhat similar to simple beats between two audible frequencies of nearly equal periodicity. When the frequencies of sources S and S are difierent from each other, there can be no pulsating current through the detecting device R, inwhich pulsations take place at regular intervals and are of equal duration, as is the case when the armatures of polar relays P and P vibrate at the same frequency and are 180 degrees out of phase. There can be no prolonged period of'silence at the detecting device R when the frequencies of the cur-' rents of sources S and S are different from each other, as is possible when the armatures of polar relays P and P vibrate at the same frequency and are out of phase by an angle different from 180 degrees.

Fig. 2 of the drawing represents another embodiment of the invention forcomparing the frequencies of two sources of current. These sources of current to be compared are designated'in this embodiment by the same reference characters, S and S The source of current of audible frequency is designated, as hereinabove, by the reference character S and reference character R designates the detecting device which may again be a telephone receiver, if desired. Two three-element vacuum tubes are shown in this embodiment of the invention, each vacuum tube including a plate, a filament and a grid. The filaments of vacuum tubes V and V are heated to electron-emitting temperatures by the current of a battery 3,. The input circuit of vacuum tube V includes the source S,, the grid and filament of vacuum tube V a battery B and the primary winding of a transformer T The input circuit of vacuum tube V, includes the source S the grid and filament of vacuum tube V battery B and the primary winding of transformer T The secondary winding of transformer T is connected to the source S The output circuit of vacuum tube V includes the filament and plate of vacuum tube V,, one-half of the primary winding of T and a battery B The output circuit of vacuum tube V includes the filament and plate of vacuum tube V the other half of the primary winding of transformer T and battery B The detecting device R is connected to the secondary winding of transformer T Battery B brings the grids of vacuum tubes V and V, to suitable potentials with respect to the corresponding filaments. Battery B provides suitable operating potentials for the plates of vacuum tubes V and V These vacuum tubes act like modulators. The detecting device R may be employed to indicate when the frequency of the currents transmitted by sources S and .S are equal, or not.

This invention provides arrangements for vcomparing the vibratory periods of two or more electrical sources. stood, however, that while the frequencies of the electrical sources to be compared are described to be below the range of audibility, 'the invention is not necessarily limited in that respect, the general principles of this invention being also applicable to systems for comparing the vibratory periods of sources within or above the range of audibility. 1

It is to be understood that if the sources to be compared are adjustable in their frequency characteristics, thegeneral rinciples of this invention may be employe to com- It will be underpare these frequencies during the period of adjustment to .determine when these frequencies become .equal. 7

While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will he understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

l. A series testing circuit comprising a first vibrating element which alternately opens and closes said circuit, a second vibrating element which also alternately opens and closes said circuit, a source of'current of audible frequency, and a detecting device through which current of the audible frc-- quency may pass for observation.

.2. An electrical testing system for comparing the frequencies of two or more generators, each of said frequencies being outside the range of audibility, a generator of current of an audible frequency, and a detecting device interconnecting all of said generators providing audible means for comparing the frequencies of said first-men'- tioned generators to determine whether or not the frequencies of said first-mentioned generators are equal and in phase.

' 3. An electrical testing system comprising a telephone receiver, a source of current of a frequency within the range of audibility of said telephone receiver and in series therewith, and two vibrating elements whose vi-' bratory characteristics are to be compared,

each of said vibrating elements periodically interrupting the current of said source.

4. An electrical testing system comprising a detecting device which may be operated by current of an audible frequency, a source of current of audible frequency in series with said detecting device, two sources of current of inaudible frequencies, and two series circuit of said detecting device and said source of current of audible frequency being connected between the armatures of said polar relays.

5. An electrical testing system for comparing the frequency characteristics of two oscillators, each frequency being below audibility, an'oscillator of current of any audible frequency, means to modify the current of the latter oscillator in accordance with the oscillations of the oscillators whose frequencies are to be compared, thereby producing current of an audible frequency appropriately interrupted, and an audible in dicating device to indicate the presence of the resultant current of audible frequency.

6. An electrical testing system comprising a detecting device, a source of current of a frequency which is readily detected by said detecting device, and two or more vibrating elements whose vibratory characteristics are to be compared, pulsations of current of variable duration being indicated at said detecting device when said vibrating elements are not isochronous.

7. The combination of a detectingdevice suchas a telephone receiver, a source of current of a frequency within the range of detection of said detecting device, and two 

